Optics Sensor Structure For Detecting Water Or Oil Leakage Inside A Conservator Having A Bladder Or Membrane

ABSTRACT

Optical sensor structure senses the presence of liquid in a sealed conservator tank. The sensor structure includes a sensor head having a body with first and second opposing ends, a plurality of perforations through the body and spaced between the first and second ends, and a mirror disposed at the second end. The perforations are constructed and arranged to receive and hold fluid therein. The sensor head is constructed and arranged to rest on a surface of a bladder. The sensor structure includes a light source, a first fiber optic cable between the light source and the first end of the body, a light detector, and a second fiber optic cable between the light detector and the first end of the body. The amount of light received by the light detector is reduced when liquid, instead of air, is in at least some of the perforations in the body.

FIELD

The invention relates to transformers and, more particularly, totransformer having a conservator oil preservation system (COPS) having abladder or a membrane, with a sensor being provided on the bladder todetect moisture on top of the bladder and/or failure of the bladder.

BACKGROUND

In the oil preservation type system, a synthetic rubber bladder, isstretched over the surface of the oil in a conservator tank tocompletely isolate the insulating oil from outside air. The bladdershape varies according to expansion and contraction of the oil,maintaining pressure in the bladder at atmospheric pressure. Since thebladder completely isolates the oil from the atmosphere, absent afailure of the bladder, there is no possibility for oxygen or moisturepenetrating the oil. Accumulation of water in a conservator tank cancontaminate the oil or can even cause confusion with respect to the oillevel indication if one believes the bladder is operating properly.

Since the conservator tanks are sealed, it is difficult to access theinside of the tank to ensure that the bladder is functioning properly toisolate the oil from the air. Thus, there is a need to provide a sensorassociated with the bladder to detect the presence of any moisture oroil on top of the bladder inside of the conservator tank.

SUMMARY

An object of the invention is to fulfill the need referred to above. Inaccordance with the principles of the present invention, this objectiveis achieved by providing optical sensor structure for sensing thepresence of liquid in a sealed conservator tank. The tank includes abladder isolating oil from air. The bladder has a first surface exposedto the air and an opposing second surface exposed to the oil. The sensorstructure includes a sensor head having a body with first and secondopposing ends, a plurality of perforations through the body and spacedbetween the first and second ends, and a mirror disposed at the secondend. The perforations are constructed and arranged to receive and holdfluid therein. The sensor head is constructed and arranged to rest onthe first surface of the bladder. The sensor structure includes a lightsource, a first fiber optic cable between the light source and the firstend of the body, a light detector, and a second fiber optic cablebetween the light detector and the first end of the body. Wherein, whenthe light source provides light through the first fiber optic cable andto the perforated body, the light reflects off the mirror and isreceived by the second fiber optic cable and by the light detector. Theamount of light received by the light detector is reduced when liquid,instead of air, is in at least some of the perforations in the body.

In accordance with yet another aspect of the invention, a method detectsthe presence of liquid on an air side of a bladder disposed in aconservator tank for a transformer oil preservation type system. Thebladder isolates oil from air and has a first surface exposed to the airand an opposing, second surface exposed to the oil. The method places anoptical sensor head on the first surface of the bladder. A source oflight is provided to the sensor head. A normal condition is determinedwhen no liquid is in contact with the sensor head by detecting a certainamount of light exiting the sensor head. A malfunction condition isdetermined when liquid is in contact with the sensor head by detectingan amount of light, less than the certain amount of light, exiting thesensor head.

Other objects, features and characteristics of the present invention, aswell as the methods of operation and the functions of the relatedelements of the structure, the combination of parts and economics ofmanufacture will become more apparent upon consideration of thefollowing detailed description and appended claims with reference to theaccompanying drawings, all of which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the following detaileddescription of the preferred embodiments thereof, taken in conjunctionwith the accompanying drawings wherein like numbers indicate like parts,in which:

FIG. 1 is a schematic view of a conservator tank fluidly coupled with atransformer tank, with optical sensor structure provided on a bladder inthe conservator tank, in accordance with the present invention.

FIG. 2 is an enlarged view of the sensor structure of FIG. 1.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

With reference to FIG. 1, transformer oil preservation type systemincludes a transformer tank 10 that is filled with insulating oil 14 toinsulate components therein, such as a tap changer (not shown). Aconservator tank structure, generally indicated at 15, includes aconservator tank 16 fluidly connected via piping 18 with the transformertank 10. A Buchholz relay 20 is provided in piping 18 in theconventional manner. An air-filled bladder 22 is stretched over thesurface of the oil 14 in the conservator tank 16 to completely isolatethe insulating oil from outside, dry air 24 air. Thus, the bladder 20has a first surface 26 exposed to the dry air 24 and an opposing secondsurface 28 contacting or resting on the oil 14. As used herein,“bladder” can be an air cell, membrane, rubber bag, or any otherstructure that can contain air and vary in shape. In the conventionalmanner, the bladder 20 shape varies according to expansion andcontraction of the oil 14, maintaining pressure in the bladder 20 atatmospheric pressure.

In accordance with the embodiment, in order to detect the presence ofwater and/or oil that has leaked past the bladder 20 due to amalfunction, tear-off, rupture, infiltration, etc., optical sensorstructure, generally indicated at 30, is provided on the first or uppersurface 26 of the bladder.

As best shown in FIG. 2, the sensor structure 30 detects light reflectedfrom a sensor head 32, when there is no moisture or insulating oil whichwould block the free path of light rays. The sensor structure 30includes a simple light emitting diode (LED) 34 as a light source thatis preferably located outside of the tank 16 at the transformer controlcabinet (not shown). The LED 34 emits light which travels through fiberoptics, generally indicated at 34, inside of the sealed conservator tank16 and connected to a first end 35 of the sensor head 32. The fiberoptics 34 is preferably an input fiber optic cable 34′ made of glass orplastic. The light-weight, sensor head 32 includes a preferably plasticbody 33 having first and second opposing ends, 35, 36. A plurality ofperforations 37 are provided through the body 33 and are spaced betweenthe ends 35, 36. The perforations 37 can receive and hold (by submersionor surface tension) oil or water that may have leaked to be above theupper surface 26 of the bladder 20 due to bladder malfunction orinfiltration, as discussed above.

Thus, the leaking oil or water that enters at least some of theperforations 37 blocks or greatly reduces the light ray reflection at aflat mirror 38 disposed at the second end 36 of the sensor head 32. Thislight reduction results because water and oil have a greater refractiveindex than air (which is in the perforations 37 when water and/or oilare not present). The reduced reflected light is captured by the fiberoptics 34 (such as output fiber optic cable 34″) which is connected to alight detector 40, preferably in the form of a photodiode or any otherphoto detector. The light detector 40 provides an electrical analogueoutput (voltage signal) any time that there is light on the surface ofthe detector 40. If no or reduced light is received by the lightdetector 40, a low voltage level is output by the light detector 40,which indicates that the perforations 37 in the sensor head 32 containliquid (water/oil) and thus there may be a malfunction of the bladder20. In the absence of any liquid inside the perforations 37 of thesensor head 32, the light rays emitted by the LED 34 reflect back fromthe surface of the mirror 38 and are captured by the fiber optic cable34″ and thus the light detector 40.

Normal voltage output indicates that air only is inside the perforationsin the sensor head (a normal operating condition with no bladder 20malfunction).

Optical insulation 42 is provided to optically isolate the LED 34 fromthe light detector 40 to avoid interference and sensor error. Forexample, the LED 34 and light detector 40 are preferably located in aself-contained sensor box (defining the optical insulation), in thetransformer control cabinet, where the minimum electronics required topower up the sensor structure 30 will be available (any DC power supplyconverted to a 5V DC or 12V DC power supply). Thus, the fiber opticcables 34′, 34″ are elongated to space the light source 34 and the lightdetector 40 remotely from the sensor head 32.

Thus, the very light-weight sensor structure 30 using fiber optics 34provides a cost-effective and efficient way to detect if water and/oilis present on the upper surface 26 of a bladder 20 of a conservator tank16. The sensor structure 20 does not interfere electrically (no currentneeded in tank 16), chemically or mechanically (weight of sensor head 32does not affect function of bladder 20), with any of the powertransformer operating parameters. The sensor structure 30 can beinstalled on the upper surface 26 of the bladder 20 in a new conservatortank, or can be dropped onto the upper surface 26 of the bladder 20 inan existing conservator tank 16 during outages.

The foregoing preferred embodiments have been shown and described forthe purposes of illustrating the structural and functional principles ofthe present invention, as well as illustrating the methods of employingthe preferred embodiments and are subject to change without departingfrom such principles. Therefore, this invention includes allmodifications encompassed within the spirit of the following claims.

1. Optical sensor structure for sensing the presence of liquid in asealed conservator tank, the tank including a bladder isolating oil fromair, the bladder having a first surface exposed to the air and anopposing second surface exposed to the oil, the sensor structurecomprising: a sensor head including a body having first and secondopposing ends, a plurality of perforations through the body and spacedbetween the first and second ends, and a mirror disposed at the secondend, the perforations being constructed and arranged to receive and holdfluid therein, the sensor head being constructed and arranged to rest onthe first surface of the bladder, a light source, a first fiber opticcable between the light source and the first end of the body, a lightdetector, and a second fiber optic cable between the light detector andthe first end of the body, wherein when the light source provides lightthrough the first fiber optic cable and to the perforated body, thelight reflects off the mirror and is received by the second fiber opticcable and by the light detector, and wherein the amount of lightreceived by the light detector is reduced when liquid, instead of air,is in at least some of the perforations in the body.
 2. The sensorstructure of claim 1, wherein the fiber optic cables are elongatedcables so as to enable the light source and light detector to be aredisposed remotely from the sensor head.
 3. The sensor structure of claim1, wherein the light source is a light emitting diode.
 4. The sensorstructure of claim 1, wherein the light detector is a photodiode.
 5. Thesensor structure of claim 1, further comprising optical insulation tooptically isolate the light source from the light detector.
 6. Thesensor structure of claim 1, wherein the liquid is water and/or oil. 7.A conservator tank structure for a transformer oil preservation typesystem, the conservator tank structure comprising: a conservator tank, abladder in the conservator tank constructed and arranged to isolate oilfrom air that is in the tank, the bladder having a first surface exposedto the air and an opposing second surface exposed to the oil, andoptical sensor structure comprising: a sensor head inside of the tankand resting on the first surface of the bladder, the sensor headincluding a body having first and second opposing ends, a plurality ofperforations through the body and spaced between the first and secondends, and a mirror disposed at the second end, the perforations beingconstructed and arranged to receive and hold liquid therein, a lightsource disposed outside of the tank, a first fiber optic cable betweenthe light source and the first end of the body, a light detectordisposed outside of the tank, and a second fiber optic cable between thelight detector and the first end of the body, wherein when the lightsource provides light through the first fiber optic cable and to theperforated body, the light reflects off the mirror and is received bythe second fiber optic cable and by the light detector, and wherein theamount of light received by the light detector is reduced when liquid,instead of air, is in at least some of the perforations in the body. 8.The tank structure of claim 7, wherein the light source is a lightemitting diode.
 9. The tank structure of claim 7, wherein the lightdetector is a photodiode.
 10. The tank structure of claim 7, furthercomprising optical insulation to optically isolate the light source fromthe light detector.
 11. The tank structure of claim 7, in combinationwith the liquid and wherein the liquid is water and/or oil.
 12. A methodof detecting the presence of liquid on an air side of a bladder disposedin a conservator tank for a transformer oil preservation type system,the bladder isolating oil from air and having a first surface exposed tothe air and an opposing, second surface exposed to the oil, the methodcomprising the steps of: placing an optical sensor head on the firstsurface of the bladder, providing a source of light to the sensor head,determining a normal condition when no liquid is in contact with thesensor head by detecting a certain amount of light exiting the sensorhead, and determining a malfunction condition when liquid is in contactwith the sensor head by detecting an amount of light, less than thecertain amount of light, exiting the sensor head.
 13. The method ofclaim 12, wherein the sensor head includes a body having first andsecond opposing ends, a plurality of perforations through the body andspaced between the first and second ends, and a mirror disposed at thesecond end, the perforations being constructed and arranged to receiveand hold liquid therein, and wherein the normal condition is determinedwhen only air is in the perforations, and the malfunction condition isdetermined when liquid is in at least some of the perforations.
 14. Themethod of claim 12, wherein the liquid is water and/or oil.
 15. Themethod of claim 12, wherein the step of providing the light sourceprovides a light emitting diode disposed outside of the tank andoptically connected to the sensor head via a fiber optic cable.
 16. Themethod of claim 12, wherein the steps of detecting light include using alight detector disposed outside of the tank and optically connected tothe sensor head via a fiber optic cable.